1. Field of the Invention
The present invention generally relates to a power supply and a method of power supplying, and more specifically to a power supply employing a regulating capacitor and a regulator connected in series to couple to an input filtering unit, and utilizing a controller to manipulate the regulator to be open circuit when a rectifying voltage generated by the input filtering unit is too high so as to switch off a conduction path from the regulating capacitor to a grounded level and prevent electrical elements from damage due to high input voltage, and a method of power supplying for operating the power supply.
2. The Prior Arts
One of the crucial components in electrical industry is a power supply, which is intended to supply stable power with appropriate voltage and/or current, particularly for normal operation under continuous or abrupt change of the input power or the loading. For example, inrush current with tens or even hundreds ampere often occurs at initially powering on, and the fuse easily melts because the rating of working power I2t is suddenly exceeded. At this time, the power supply does not provide desire power and the normal operation and function of the application system are terminated. Furthermore, inrush current carries a very huge peak, which easily burns out all electrical elements configured in the rectifying bridge, switching transistor or clamping circuit, and even large noise interference is induced to affect other electronic devices using the same common power.
In the prior arts, a thermistor or called NTC (negative temperature coefficient) resistor is commonly used to suppress inrush current at powering on. Specifically, the thermistor exhibits the property of negative temperature coefficient. In other words, as the temperature of the thermistor increases, the resistance of the thermistor decreases. Thus, for most low-end applications, the thermistor is a practical solution for solving inrush current.
Further, the operation of the thermistor is described as below. The thermistor is serially inserted into the alternating power line or the DC line of the bridge type rectifier. When the power supply is initially powered on and the Buck-Cap is charged, the total impedance of the input line is about the sum of ESR of the capacitor and the impedance of the thermistor, that is, ESR+RRT. At this time, the current flowing through the input line is not large because the impedance is not over low. As the temperature of the thermistor increases, the resistance fast decreases to the lowest value. When the Buck-Cap is fully charged, the total power consumption does not increase a lot by the thermistor. Therefore, the thermistor indeed improves efficiency of power utilization.
However, one shortcoming in the prior arts is that the thermistor substantially still has some resistance and impedance such that the overall efficiency of the power supply can not be further improved. Moreover, high voltage elements are needed to avoid damage by inrush current, and the hardware cost thus increases. As a result, the above scheme with the thermistor in the prior arts is adverse to industrial applications.
Therefore, it is greatly needed to provide a new power supply and method of power supplying, employing a controller to manipulate a regulator to perform one of working modes of initial open circuit, power on conduction, short circuit normal operation and over-voltage open circuit protection so as to reduce inrush current upon powering on and prolong lifetime of electrical elements, thereby overcoming the above problems in the prior arts.